Which of the following is an example of a folksonomy?

Visitors to Amazon's site can use its search engine to find a book by using the search term of "can't wait to read."

The Google Documents software that enables multiple users in different locations to work on the same file is an example of social software.

Internet users create, publish, rate, edit, and share information with Wikipedia.

Second Life and Web Alive allow people to participate as avatars.